GPFSeminars 2009

Time: 25. December 2009, 14:00hPlace: Institute of Physics, room 300Speaker: Vladimir JuricicTitle: Electrons on a hexagonal lattice: interactions, symmetries and phase transitionsAbstract:
In this talk, I will discuss general theory of the local repulsive short-range electron interactions on the graphene's honeycomb lattice. I will show how various symmetries dictated by the underlying lattice together with algebraic relations between different local fermionic quartic terms, namely the Fierz identities, restrict the form of the low-energy Hamiltonian. Possible semimetal-insulator quantum phase transitions will then be considered in the framework of an effective Gross-Neveu-Yukawa theory using an epsilon expansion near three spatial dimensions [2]. Finally, I will briefly address the role of the long-range Coulomb interaction at the quantum critical point near lower critical dimension of the theory [3].
References:
[1] I. F. Herbut, V. Juricic, and B. Roy, Phys. Rev. B 79, 085116 (2009).
[2] I. F. Herbut, V. Juricic, and O. Vafek, Phys. Rev. B 80, 075432 (2009).
[3] V. Juricic, I. F. Herbut, and G. W. Semenoff, Phys. Rev. B 80, 081405(R) (2009).

Time: 4. December 2009, 11:00hPlace: Institute of Physics, room 300Speaker: John MadoreTitle: Noncommutative spherical symmetryAbstract:
The algebra and calculus for the static spherically symmetric configuration of the gravitational field are given. The radial variable takes its values in a discrete subset of the positive real line. The most general solution we have found contains 4 real parameters. The identification of these with the mass and cosmological constant still remains to be done.

Time: 27. November 2009, 11:00hPlace: Institute of Physics, room 300Speaker: Maja BuricTitle: Lectures on fuzzy sphere - part 4Abstract:
The idea of this sequence of 3-4 lectures is to describe results and give an
overview of papers related to fuzzy sphere.
Lecture 1: geometry of the fuzzy sphere
Lecture 2: classical gauge and fermionic fields
Lecture 3: classical and quantum scalar field

Time: 20. November 2009, 11:00hPlace: Institute of Physics, room 300Speaker: Maja BuricTitle: Lectures on fuzzy sphere - part 3Abstract:
The idea of this sequence of 3-4 lectures is to describe results and give an
overview of papers related to fuzzy sphere.
Lecture 1: geometry of the fuzzy sphere
Lecture 2: classical gauge and fermionic fields
Lecture 3: classical and quantum scalar field

Time: 13. November 2009, 11:00hPlace: Institute of Physics, room 300Speaker: Maja BuricTitle: Lectures on fuzzy sphere - part 2Abstract:
The idea of this sequence of 3-4 lectures is to describe results and give an
overview of papers related to fuzzy sphere.
Lecture 1: geometry of the fuzzy sphere
Lecture 2: classical gauge and fermionic fields
Lecture 3: classical and quantum scalar field

Time: 6. November 2009, 11:00hPlace: Institute of Physics, room 300Speaker: Maja BuricTitle: Lectures on fuzzy sphere - part 1Abstract:
The idea of this sequence of 3-4 lectures is to describe results and give an
overview of papers related to fuzzy sphere.
Lecture 1: geometry of the fuzzy sphere
Lecture 2: classical gauge and fermionic fields
Lecture 3: classical and quantum scalar field

Time: 23. October 2009, 11:00hPlace: Institute of Physics, room 300Speaker: Marko SimonovicTitle: Mass and Charge of the Electron in Gravity-modified Quantum ElectrodynamicsAbstract:
In this paper the model of gravity-modified quantum electrodynamics has been studied. Lagrangian of the theory has been built starting from quantum electrodynamics on one side and general theory of relativity on the other. The propagators for electromagnetic and gravitational field have been found using field-antifield method. Self-energy diagrams for electron and photon have been analyzed in lowest order of perturbation theory, it has been given detailed derivation of graviton superpropagator that appears in this processes and it has been shown how reciprocal value of gravitational constant plays roll of cut-off parameter in equations for renormalised mass and charge of the electron.

Time: 16. October 2009, 11:00hPlace: Institute of Physics, room 300Speaker: Dragan PrekratTitle: Sparkling horizonAbstract:
Short summary of the graduate thesis with topic in Hawking radiation. Derivation of Unruh effect in 2D for the hyperbolic observer and massless scalar field, and discussion of its connection to the Hawking radiation.

Time: 2. October 2009, 11:00hPlace: Institute of Physics, room 300Speaker: Ljubica DavidovicTitle: The Moyal and Wick-Voros star productsAbstract:
We discuss the properties of the Moyal and Wick-Voros star products and compare the noncommutative field theories built using these two star products.

Time: 25. September 2009, 11:00hPlace: Institute of Physics, room 300Speaker: Marko VojinovicTitle: Introduction to Turaev-Viro invariant and applications to
physicsAbstract:
We give an non-rigorous introduction to Turaev-Viro invariant, and sketch a proof of invariance. The emphasis will be on intuitive geometric interpretation. We also briefly describe its physical meaning and applications within the framework of Loop Quantum Gravity.

Time: 18. September 2009, 11:00hPlace: Institute of Physics, room 300Speaker: Branislav CvetkovicTitle: Asimptotic structure of topologically
massive gravity in "spacelike stretched" AdS sectorAbstract:
We introduce a natural set of asymptotic conditions in the spacelike stretched AdS sector of topologically massive gravity. The Poisson bracket algebra of the canonical generators is shown to have the form of the semidirect sum of a u(1) Kac-Moody and a Virasoro algebra, with central charges. Using the Sugawara construction, we prove that the asymptotic symmetry coincides with the conformal symmetry, described by two independent Virasoro algebras with central charges. The result is in complete agreement with the hypothesis formulated by D. Anninos et al.

Time: 4. September 2009, 11:00hPlace: Institute of Physics, room 300Speaker: Aleksandar MikovicTitle: Spin foam perturbation theory and quantum gravityAbstract:
In this seminar we shall give an overview of spin foam perturbation theory in d=3,4 and the connection with quantum theory of gravity.

Time: 8. May 2009, 11:00hPlace: Institute of Physics, room 300Speaker: Larisa JonkeTitle: Homolumo Gap and Matrix ModelAbstract:
After short introduction into matrix models, we introduce a dynamical matrix model by which probability distribution is associated with Gaussian ensembles from random matrix theory. We interpret the matrix M as a Hamiltonian representing interaction of a bosonic system with a single fermion. We show that a system of second-quantized fermions influences the ground state of the whole system by producing a gap between the highest occupied eigenvalue and the lowest unoccupied eigenvalue.

Time: 20. March 2009, 11:00hPlace: Institute of Physics, Library RoomSpeaker: Branko DragovicTitle: Nonlocal Lagrangians for p-Adic StringsAbstract:
p-Adic strings are important objects of string theory, as well as of p-adic mathematical physics and nonlocal cosmology. By a concept of adelic string one can unify and simultaneously study various aspects of ordinary and p-adic strings. By this way, one can consider adelic strings as a very useful instrument in the further investigation of modern string theory. It is remarkable that for scalar p-adic strings exist effective Lagrangians, which are based on real instead of p-adic numbers and describe not only four-point scattering amplitudes but also all higher ones at the tree level. In this talk, we will ﬁrst give a review of p-adic strings and their Lagrangians. Then, starting from p-adic Lagrangians, we consider some approaches to construction of effective ﬁeld Lagrangians for p-adic sector of adelic strings. It yields nonlinear and nonlocal scalar ﬁeld theory Lagrangians, where spacetime nonlocality is determined by an inﬁnite number of derivatives contained in the operator-valued Riemann zeta function. Owing to the Riemann zeta function in the dynamics of these scalar ﬁeld theories, obtained Lagrangians are also interesting in themselves.

Time: 27. February 2009, 11:00hPlace: Institute of Physics, room 300Speaker: Maja BuricTitle: Geometry of the Grosse-Wulkenhaar ModelAbstract:
We define a two-dimensional noncommutative space as a limit of finite-dimensional matrix spaces and show that it is a `natural' geometry for the Grosse-Wulkenhaar scalar field model, i.e. that the Grosse-Wulkenhaar (renormalizable) action is the action for the scalar field coupled to the curvature of this space.

Time: 6. February 2009, 12:00hPlace: Institute of Physics, room 300Speaker: Bojana FemicTitle: Hopf algebras and their appearance in physicsAbstract:
In this lecture we shall present the definition and basic notions of Hopf algebras, as well as some examples. Some subjects of investigation of Hopf algebras in mathematics and their applications in physics shall be discussed. These and similar related topics could be considered in possible following lectures.

Time: 16. January 2009, 11:00hPlace: Institute of Physics, room 300Speaker: Stanko PetkovicTitle: The Casimir effectAbstract:
We analyze the Casimir force between two planes using the real scalar field model. The sketch of the derivation of Euler-Maclaurin formula using the Bernoulli polynomials will be given.